High molecular weight light emitting materials and charge transport materials are, in contrast to the corresponding low molecular weight materials, soluble in solvents and hence, with the aid of coating methods, can form light emitting layers and charge transport layers in light emitting devices. Therefore, various investigations have been carried out on these high molecular weight materials. As polymer materials which can be used as light emitting materials and charge transport materials for EL devices, polyphenylene vinylene derivatives, polyfluorene derivatives, polyphenylene derivatives and the like have hitherto been known. On the other hand, a copolymer is well known in the art which comprises 9-oxo-9-phosphafluorene-2,7-diyl units and arylene units in the main chain thereof (Proceedings of the 79th Annual Spring Meeting of the Chemical Society of Japan, 2001, 3D209, p. 821); however an EL device has not been known yet which uses a copolymer comprising 9-oxo-9-phosphafluorene-2,7-diyl units as the main chain thereof.